Many different types of electronic devices include an electronic visual display that can provide visual information to a user. For example, a liquid-crystal display (LCD) is a widely used type of display that can be found is a wide range of electronic devices, including digital cameras, watches, calculators, and mobile telephones, including smartphones. An LCD is a flat-panel display that is often a desirable display option for several reasons, which may include that LCDs are relatively thin, light-weight, and efficient in terms of power consumption. In addition, the LCDs are known to have high resolution, high color display, and high definition.
The LCD in most electronic devices is part of an LCD module that has an LCD panel and a built-in driving circuit unit. The LCD panel typically includes a thin-film transistor (TFT) array substrate, a color filter substrate, a liquid crystal layer located between the TFT array substrate and the color filter substrate, and a backlight assembly disposed under the LCD panel to serve as a light source. The driving circuit unit typically includes an LCD Driver Integrated Circuit (driver IC) disposed at an outer ring of the LCD panel to drive the LCD panel. The LCD panel includes pixels in a matrix shape between two glass substrates (the TFT array substrate and the color filter substrate mentioned above) with a switching device for controlling signals respectively supplied to the pixels, like a thin-film transistor. An array of pixels is disposed between the two glass substrates in a matrix pattern on the TFT array substrate. A switching element, such as a TFT, is provided for each pixel for controlling drive signals to the respective pixel.
The driving circuit unit includes the above-mentioned driver IC, as well as a printed circuit board (PCB) on which driving circuits are provided for generating various signals for driving the LCD panel, such as control signals, clock signals, and data signals. The driver IC is connected to the LCD panel and the PCB to apply a signal to the TFTs, storage capacitors, pixel electrodes, and interconnect wiring of the LCD panel. The interconnect wiring includes gate bus-lines and data bus-lines arranged so that each pixel is individually addressable by the driving circuit unit. The driver IC includes a set of bonding pads with each bonding pad including a metal bump. The surface to which the driver IC is to be mounted is provided with a matching set of pads. The driver IC is mounted on the surface by bonding the set of bonding pads to the matching set of pads.
Chip On Glass (COG) and Chip On Film (COF) are two common methods for mounting a driver IC and connecting it to control an LCD panel. COG is a flip-chip bonding technology where the driver IC is mounted to a non-display region of the LCD panel's array substrate using Anisotropic Conductive Film (ACF). COF is also a flip-chip bonding technology, but the driver IC is mounted to a flexible printed circuit board (FPC), which in turn is mounted to a non-display region of the LCD panel's array substrate. This is undesirable because it results in LCD modules and LCD panels that have an overall footprint that is larger than that the actual display and dead edge regions that get covered for aesthetic reasons in the final product (e.g., smartphone or tablet computer).
FIGS. 1 and 2 illustrate an example of the non-display region caused by installation of a driver IC using a COG arrangement. FIG. 1 shows a perspective view of a display module 100, which illustrates an example of COG technology. The display module 100 includes an LCD panel 102, a driver region 104, and an FPC 106.
The LCD panel 102 is a multi-layer assembly that includes a stacked pair of transparent (with light transmissivity) glass substrates—an array substrate 108 and a filter substrate 110—that are separated by a liquid crystal layer (not shown). The liquid crystal layer contains liquid crystal molecules, which are substances that change optical characteristics when an electromagnetic field is applied. The manufacturing process includes injecting liquid crystal into a gap between the TFT array substrate 108 and the color filter substrate 110, thereby producing the LCD panel 102.
The array and filter substrates each include an aligned array of transparent electrodes that can apply electromagnetic fields to control the optical characteristics of a small respective area of liquid crystal material between the electrodes. Each electrode on the array substrate is associated with a respective transistor, for example a thin field transistor (TFT). The strength of the electromagnetic field between a pair of array substrate and filter substrate electrodes depends on the state of the respective TFT, which in turn depends on drive signals sent from the driver region 104. The filter substrate 110 is also a color filter substrate 110 in that it includes a respective color filter (not shown) for each pixel to add color to the displayed image.
The driver region 104 is a region of the LCD module 100 that provides a mounting location for a driver IC 112 (shown in FIG. 2). The driver IC 112 is an LSI chip including a driver circuit therein. The driver IC 112 is configured to operate based on signals (e.g., image data) from a remote signal source (not shown). The remote signal source can vary depending on the application. The driver IC 112 is configured to generate output drive signals from the input image signals, and to send the output drive signals to the display area of the liquid crystal panel 102. The driver 102 is directly mounted on the array substrate 108 of the liquid crystal panel 102 in a non-display area, that is, through a chip on glass (COG) mount method.
FIG. 2 shows a partial side view of the portion of the display module 100 near the driver IC 112. The driver IC 112 is a source driving integrated circuit package mounted on data lines. The driver IC 112 receives image signals via the image signal input bumps 114, converts the received image signals into corresponding drive signals (e.g., voltage or current signal), and transmits the drive signals to the LCD panel 102 via the driving signal output bumps 116.
The image signal input bumps 114 are connected to conductive patterns 118, which are in turn connected to the FPC 106 via an anisotropic conductive film (ACF) 120. The driving signal output bumps 116 are connected to data lines 122 via the anisotropic conductive film 120. The TFT array substrate 108 supports the conductive patterns 120 and data lines 122, as shown.
Thus, while the use of the display module 100 provides the convenience of an LCD panel 102 with an integrated driver IC 112, this technology still has several drawbacks that leave room for improvements. The technology involves several complicated and expensive types of connections and component mounting techniques, and the driver region of the array substrate creates dead space that prevents use of the entire display-module footprint as actual display area.
It would therefore be desirable to improve on prior LCD packaging technologies to reduce cost and dead space for the display. The present disclosure provides novel packaging technologies that include such desired improvements.